This application claims the benefit of Korean Application No. 2001-49866, filed Aug. 26, 2000, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to compensating for disturbances in an optical recording/reproducing apparatus using learning control, and more particularly, to an apparatus and method for compensating for disturbances, such as eccentricity in a disk drive system of the optical recording/reproducing apparatus by performing feed-forward control using an iterative learning method, storing a result of the feed-forward control, and applying the result of the feed-forward control to a compensator to compensate for disturbances.
2. Description of the Related Art
FIG. 1 shows an example of a tracking error signal generated due to eccentricity in an optical recording medium. Eccentricity occurring in the optical recording medium is due to a rotation shaft of a spindle inconsistently rotating a disk at a center of a track of the disk. In an optical recording medium drive system, the eccentricity of the optical recording medium has served as an important periodic disturbance factor, and its influence increases with an increase in speed multiple. Accurately following the track of the disk cannot be accomplished without compensating for the eccentricity. Accordingly, conventional systems have utilized various eccentricity compensation methods.
FIG. 2 is a block diagram of a pickup head (PUH) position control system in a typical optical recording/reproducing apparatus. The PUH position control system receives a position command directing a pickup head (not shown) to be positioned at a desired location. A signal representing an actual position of an actuator 220 of an optical recording medium drive for moving the pickup head is fed back in a negative direction and added to a position command signal in an adder 200. An error signal e output from the adder 200 is applied to a controller 210. The controller 210 performs a predetermined algorithm for compensating for the error signal e, and outputs a compensated signal to the actuator 220. The actuator 220 moves the pickup head in response to the compensated signal received from the controller 210. These operations are repeated, and thus the position of the pickup head is adjusted. However, this control system cannot deal with a disturbance, such as a large eccentricity.
FIG. 3 is a block diagram of an embodiment of a conventional PUH position control system in which a routine for performing disturbance compensation is added to the control system of FIG. 2. In this system, a compensation routine 300 is performed on the assumption that a perfect sine wave Asin(xcfx89t+"psgr") is an eccentricity signal, having an eccentricity of A, a disk rotation frequency xcfx89, and an eccentricity phase "psgr". This compensation method is disclosed in U.S. Pat. No. 5,892,742, which is hereby incorporated by reference. In the operation of the system of FIG. 3, a feed-forward control input is calculated from an error waveform, as shown in FIG. 1, before control of tracking starts. That is, the size of the eccentricity is determined by a number of track errors generated during one rotation of a spindle over a track (i.e., during a cycle) shown in FIG. 1, and a phase of eccentricity is determined by a spindle index reference signal representing one rotation and a delay time at which the period of the track error is greatest. The thus-calculated feed-forward control input is added to the output of the controller 210 of FIG. 3 to accomplish a track error compensation including compensation of eccentricity. This disturbance compensation method is very simply performed and so it can be easily applied. However, this disturbance compensation method is an open-loop control method, which does not consider the response characteristics of an existing servo (actuator) control system. There is a limit in the performance of the disturbance compensation method since periodic disturbances including eccentricity are not perfect sine waves.
FIG. 4 is a block diagram of another embodiment of a conventional PUH position control system in which a routine for performing disturbance compensation is added to the control system of FIG. 2. The system of FIG. 4 is disclosed in U.S. Pat. No. 5,550,685, which is hereby incorporated by reference, and is applied to hard disk drive systems. In this control system, first, a fixed feed-forward control input is obtained using a track error signal and stored in a table 400 prior to starting control. Then, upon control, errors generated due to disturbances are compensated using the stored control input. This control system also includes a separate adaptive feed-forward control unit 410 in preparation for changes in characteristics of repeatable run out (RRO) caused by external factors during operation of a drive system. A discrete Fourier transform (DFT) and an inverse discrete Fourier transform (IDFT) are sequentially performed to extract a specific frequency component from a position error signal PES, thereby obtaining a signal with a specific frequency component. The obtained specific frequency component signal is added to the error input of an existing servo control loop. In this way, error compensation control can be accomplished.
The system of FIG. 4 is complicated since it accomplishes error compensation control in consideration of the entire closed-loop response characteristics, but can be considered a more effective disturbance compensation system than FIG. 3. However, the system of FIG. 4 considers only disturbances of a specific frequency component rather than disturbances with all frequency components actually present in a control region of the disk drive system, and it is difficult to cope with changes in a cycle such as variations in the speed multiple.
Therefore, in a periodic system such as the disk drive system, calculations of a control input in consideration with all frequency components within a control region is necessary for a high-performance disturbance compensation operation. Also, new disturbance compensation methods and apparatuses are required to effectively cope with changes in system cycle caused by a variation of the speed multiple and a variation of a control mode.
Various objects and advantages of the invention will be set forth in part in the description that follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To solve the above problem, an objective of the present invention is to provide an apparatus and method of compensating for disk disturbances having periodic disturbances with all frequency components within the control region of an optical recording medium drive servo system and considering variations in the rotation speed multiple of the optical recording medium in an optical recording/reproducing apparatus.
To achieve the above and other objectives, the present invention provides an optical recording medium drive servo system of an optical recording/reproducing apparatus having a head, the system including an actuator moving a position of the head for recording data on a recording medium or reproducing the recorded data from the recording medium; an error detector detecting a position error including a difference between a reference position on the recording medium and an actual position of the head; a compensator receiving the position error from the error detector and producing a value therefrom to drive the actuator; a first memory storing control inputs for compensating for the position error of the actuator due to a disturbance; a second memory converting the control inputs of the first memory according to a phase and storing converted control inputs; a timing controller generating addresses for the first memory and the second memory according to the phase; and an adder adding the control inputs of the first memory or the converted control inputs of the second memory to the driving value from the compensator and providing a resulting sum to the actuator to compensate for the disturbance.
The first memory stores the control inputs to compensate for the position error generated during a predetermined rotation period of time through repeated operations of updating the control inputs stored in the first memory unit with a sum of a position error filtered value and a filtered value of the control inputs stored in the first memory unit, the operations being repeated until the position error is at or below a predetermined value.
A first filter filtering the position error value; and a second filter filtering the control inputs stored in the first memory, wherein a filtering coefficient is determined for the first and second filters, so that the sum is converged as a number of repetitions of the operations increases.
The timing controller generates an address for the first memory corresponding to a number of samples of position errors generated during one rotation cycle using a frequency generator pulse (FG) of a spindle motor for rotating the recording medium for the first memory and generates an address for the second memory corresponding to a number of rising edges and falling edges of the FG generated during the one rotation cycle.
The optical recording medium drive servo system may further include an interpolator interpolating the control inputs stored in the addresses of the second memory before the control inputs of the second memory is applied to the adder.
The optical recording medium drive servo system may further include a multiplexer outputting the control inputs of the first memory to the adder during a process in which the control inputs are stored in the first memory until position errors are converged to a predetermined value, and outputting interpolated control inputs from the interpolator after the process.
To achieve the above and other objectives, the present invention also provides a disturbance compensation module using learning control, for generating a control input to compensate for track position errors due to a periodic disturbance occurring in an optical recording medium in an optical recording medium drive servo system of an optical recording/reproducing apparatus, the module including: a first filter filtering the track position errors; a memory storing control inputs for compensating for a track control cycle in a corresponding address, wherein the memory includes addresses, a number of which corresponds to a number of samples of the track position errors; a second filter filtering the control inputs stored in the memory; and an adder adding the filtered track position errors from the first filter to the filtered control inputs from the second filter and outputting a result of the addition to the memory, updating the control inputs to compensate for the track control cycle. The control inputs previously stored in the memory are updated with the result from the adder until the track position error is at or below a predetermined value.
The disturbance compensation may further include a a second memory storing final control inputs for compensating for the track control cycle in response to a pulse edge timing generated during a one track control cycle; and an interpolator interpolating the final control inputs stored in the second memory, wherein a track position control is made using the interpolated final control inputs to control the tracks on the optical recording medium.
To achieve the above and other objectives, the present invention also provides a disturbance compensation module using learning control, for generating a control input to compensate for track position errors due to a periodic disturbance occurring in an optical recording medium in an optical recording medium drive servo system of an optical recording/reproducing apparatus, the module including: a first filter filtering the track position errors; a first memory comprising addresses, the number of which corresponds to a number of samples of the track position errors, and storing control inputs for compensating for a track control cycle in the addresses; a second filter filtering the control inputs stored in the memory; an adder adding the filtered track position errors from the first filter to the filtered control inputs from the second filter and outputting a result of the addition to the first memory; a second memory storing final control inputs for compensating for the track position errors in response to a pulse edge timing generated during a one track control cycle; and an interpolator interpolating the final control inputs stored in the second memory, wherein the control inputs previously stored in the first memory are updated with the result from the adder until the track position error is at or below a predetermined value, and a track position control is made using the interpolated final control inputs to control tracks on the optical recording medium.
The disturbance compensation module may further include a multiplexer multiplexing the control inputs stored in the first memory to obtain an error-compensation control input value for a track position control during the one track control cycle and the interpolated final control inputs from the interpolator after all control inputs for disturbance compensation during the track control cycle are obtained and stored in the first memory.
To achieve the above and other objectives, the present invention also provides a disturbance compensation method using learning control generating a control input for compensating for track position errors due to a periodic disturbance occurring on an optical recording medium, the method including: determining whether a control input for disturbance compensation is required; obtaining a feed-forward control input to compensate for a track control cycle on the optical recording medium determined when the control input is determined to be required; converting the feed-forward control input into the control input depending on a phase of a track driving spindle and storing the converted control input value; and compensating for the track position errors generated due to the disturbance using the converted control input.
The method further including determining that a disturbance compensation control input is required when a magnitude of the track position error is equal to or greater than a predetermined value, wherein the track position errors on the optical recording medium is measured prior to controlling tracking in the optical recording medium are measured equal to or greater than a predetermined value, it is determined that a disturbance compensation control input is required].
A control process is one rotation of a track on the optical recording medium and when a k-th attempted control input result is uk(t) and the track position error measured is ek(t), a (k+1)th attempted control input result uk+1(t) is calculated using a following equation:
Uk+1(s)=P(s)Uk(s)+Q(s)Ek(s)
wherein Uk+1(s), Uk(s) and Ek(s) denote Laplace transforms of uk+1(t), uk(t) and ek(t), respectively, and P(s) and Q(s) denote functions representative of a predetermined filter characteristic determined so that Uk+1(s) is converged, and a final periodic feed-forward control input is obtained by repetitive operations of the equation.
The feed-forward control input is adapted to compensate for the track position errors, until the final feed-forward control input is obtained, and the control input converted according to the phase is adapted to compensate for the track position error after the final feed-forward control input generated during the track control cycle is obtained.
The method further includes interpolating the stored values and outputting the interpolated values to a disturbance compensation control input.
The present invention also provides for a method for an optical recording medium drive servo system of an optical recording/reproducing apparatus having a head, the method including: moving a position of the head for recording data on a recording medium or reproducing the recorded data from the recording medium; detecting a position error including a difference between a reference position on the recording medium and an actual position of the head; receiving the position error and producing a value therefrom to drive a disk drive system; storing control inputs to compensate for the position error due to a disturbance; converting the control inputs stored according to a phase and storing converted control inputs; generating addresses for the control inputs stored and the converted control inputs according to the phase; and adding the control inputs stored or the converted control inputs to the value to drive the disk drive and providing a resulting sum to the disk drive system to compensate for the disturbance.
The present invention also provides for a method for generating a control input to compensate for track position errors due to a periodic disturbance occurring in an optical recording medium in an optical recording medium drive servo system of an optical recording/reproducing apparatus, the method including: filtering the track position errors; storing control inputs for compensating for a track control cycle in a corresponding address and storing addresses, a number of which corresponds to a number of samples of the track position errors; filtering the control inputs stored; adding the filtered track position errors to the filtered control inputs; and outputting a result of the addition to update the control inputs to compensate for the track control cycle.
These together with other objects and advantages, which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.